Ballast material selection: The ballast packed under and around sleepers to transfer loads to the formation commonly consists of which materials?

Introduction / Context:
Ballast provides load distribution, drainage, and track resilience. Selection depends on availability, cost, and performance. While broken stone is preferred for main lines, gravel and moorum can be used in lower category lines or as sub-ballast and shoulders.

Given Data / Assumptions:

• Conventional ballasted track structure.
• Requirement for drainage, interlock, and resilience.
• Regional material availability considered.

Concept / Approach:
Broken stones (angular) interlock well and provide superior stability and drainage. Gravels can function where stone is scarce. Moorum (weathered lateritic material) is sometimes used as sub-ballast or in yards with low speeds. Hence, multiple materials may be adopted depending on service conditions.

Step-by-Step Solution:
1) Identify performance needs: strength, drainage, maintainability.2) Evaluate material properties: angularity, durability, permeability.3) Conclude that broken stone, gravel, and moorum are all used in practice, with broken stone preferred for high-speed/mainline.

Verification / Alternative check:
Maintenance manuals specify preferred gradations for stone ballast and acceptable substitutes for lower classes of track.

Why Other Options Are Wrong:

• Cement mortar is not a ballast; it would create rigid support and block drainage.

Common Pitfalls:

• Using rounded river pebbles without adequate angularity leads to poor interlock.
• Ignoring proper gradation and fouling control causes drainage issues.

Final Answer:
All of the above.